Bacillus thuringiensis (B.t.) is widely used for the microbial control of insects. The active component has been identified as a proteinaceous paraspore also described as a crystal. Following ingestion by the insect host the crystal is processed by gut proteases to the active protease-resistant form which is toxic. Toxicity is postulated to follow binding of the active form of the toxin to the insect cells resulting in disruption of cellular integrity through a receptor mediated process (Knowles, B.H. et al. [1984] FEBS 168:197-202).
A comparison of amino acid sequence for the protease activated form of B. thuringiensis var. kurstaki HD-1 and HD-73 reveals that the amino-terminal (N-terminal) half of the protein is highly conserved whereas the carboxy-terminal (C-terminal) is highly substituted in sequence. In U.S. Pat. No. 4,467,036 B. thuringiensis var. kurstaki HD-1 is disclosed as being available from the NRRL culture repository at Peoria, Ill. Its accession number is NRRL B-3792. B. thuringiensis var. kurstaki HD-73 is also available from the NRRL under accession number NRRL B-4488.
In addition to HD-1 and HD-73, the presence of an N-terminal conserved or constant region and a C-terminal highly substituted or variable region in the active toxin has been demonstrated for B. thuringiensis var. berliner and var. aizawa.
Schnepf, E. H. and Whitely, H. R. (1985) J. Biol. Chem. 260:6273-6290 have demonstrated that deletions of the amino and carboxy termini result in a loss of toxicity indicating that both regions of the active toxin are required for toxicity.